The present invention relates to a thin-film magnetic material having a high coercivity, and more particularly to a thin film of high coercivity or thin-film permanent magnet made of a Co-Pt alloy and a method of producing the same.
Magnetic recording techniques employing magnetic discs and magnetic tapes have had the magnetic recording density enhanced every year, and magnetic recording materials and magnetic recording systems have been improved or bettered accordingly.
Regarding the magnetic discs and magnetic tapes which have hitherto been .gamma.Fe.sub.2 O.sub.3 coating media, iron powder coating media and oblique deposition film media of high coercivity are being developed for the magnetic tapes, while .gamma.Fe.sub.2 O.sub.3 film media produced by the combination of sputtering and heat treatment, etc., are being developed for the magnetic discs. Although magnetic characteristics required of permanent magnet films for these magnetic recording media are somewhat different depending upon intended uses, it is a feature that the coercivity and the remanence are greater than those of the conventional materials in any application. In addition, as regards a thin-film magnetoresistance element, there is a method in which a bias field is applied by a permanent magnet film, and also the permanent magnet film for this element is required to be great in the coercivity and the remanence.
Meanwhile, as a bulky Co-Pt-based magnet, there has been known a CoPt magnet which contains 50 atomic-% of Pt, the balance being Co. It is usually quenched at 1,000.degree.-1,200.degree. C., whereupon it is tempered at 600.degree.-850.degree. C. and has the coercivity increased by aging. This is based on the formation of the ordered phase of CoPt, and can be realized in only a composition range very close to the aforementioned composition. It is said that the CoPt ordered-type permanent magnet can be produced also in the form of a thin film. According to Japanese Laid-Open Patent Application No. 50-140899, a thin film made up of 70-85 weight-% of Pt and 35-15 weight-% of Co can have the coercivity increased by an ordering treatment similar to that of the bulky material described above, and the maximum value of 2,300 Oe is obtained as the coercivity. There is also an example in which a Co-Pt film has been formed by a plating process (V. Tutovan; Thin Solid Films, 61 (1979), 133), but the coercivity is, at most, approximately 300 Oe. This is not considerably different from the magnitudes of the coercivity of the Co simple substance which are obtained by adjusting the atmosphere of evaporation, etc., and an effect based on the addition of Pt cannot be said remarkable.
As described above, the prior art requires the heat treatment in order to produce the thin-film magnetic material having the high coercivity. For this reason, not only the production cost rises, but also a substrate with the magnetic material film deposited thereon is adversely affected by the heat treatment. Further, the magnetic material and the substrate sometimes react due to the heat treatment, resulting in a change in the quality of the magnetic material film.
The following references are cited to show the state of the art; i) Official Gazette of Japanese Laid-Open Patent Application No. 50-140899, ii) Thin Solid Films, Vol. 61 (1979), pages 133-140.